In the following, the description will be directed to the application of the screen printing method according to the present invention to a window shutter; however, said method should not be considered in any way limited to this specific use, being it applied to any other support other than a window shutter.
Several screen printing methods are known.
Normally, traditional screen printing methods involve the use of a fabric arranged stretched on a frame hinged to a lower base, on which the piece, or the support, to be decorated is placed.
Before proceeding to screen printing, the above fabric is cut so as to create in it areas permeable and other areas impermeable to the ink, thereby forming a so-called matrix image.
Once the fabric is rested on a surface of the piece to be decorated and poured ink on the side of the fabric opposite to the workpiece, it is obtained the image formation on said surface, due to the passage of the ink through the permeable areas of the fabric.
Currently there are several ways to prepare a screen printing image matrix.
The easiest method to prepare a image matrix is to draw it by hand on paper or on a film in the desired form and size, cutting it and sticking it on the frame, or drawing the image negative directly on the frame and applying a filler material that becomes waterproof, when it is dry, on the parts outside of the drawing.
Another technique, however more complex, to prepare an image matrix is to draw the image on a fabric print with a special fluid, letting it dry and completely cover the aforementioned fabric with a waterproof material. After fluid drying, water is sprayed on the fabric, in such a way that the areas previously covered with the fluid to be cleaned and, therefore, made free for the following passage of the ink, leaving the other areas covered.
The image matrix can be alternatively realized by direct engraving systems. These systems, commonly referred by the acronym CTS (Computer To Screen) in the field jargon, have the advantage of being repeatable digital processes, which do not require the use of films.
For multi-color screen prints the use of more matrices (one for each color) is provided, for which, during printing, it is necessary to keep a perfect print register.
Normally, the screen printing frame is made of a fabric of very fine and regular yarn, arranged stretched on an aluminum, iron or sometimes wood frame.
In the past, the traditionally used fabric in screen printing was the silk; today, however, in its place nylon or polyester are used.
As described above, in screen printing certain areas of the printing fabric are “blocked”, or made waterproof to the ink, for composing a predetermined image. In this way, the “blocked” fabric parts do not appear in the print on the target support. Differently in the free, or permeable, parts of the fabric, the ink passes through the tiny holes of the cavities formed by the weft and warp threads, to deposit on the surface of the support to be decorated.
The so treated fabric takes, generally, the name of image array.
The screen printing techniques normally used in industrial processes provide the use of photosensitive dichromate or diazo gelatin, as substances for the formation of the waterproof areas in the image matrices.
Once the image is drawn or transferred on the printing fabric by one of the traditional techniques, it is placed on the support to be decorated. At this point, the ink is poured over the fabric, precisely on the side of the fabric opposite to the support to be decorated, and with a rubber spatula, even called “squeegee”, it is spread over the entire surface of the same, including the open areas to the substrate.
In this way, the ink passes through the open spaces and is deposited on the underlying substrate, such as paper, canvas, cloth.
After the ink transfer from the printing fabric to the selected support, the latter is dried, while the frame may be subjected to cleaning for a possible later reuse.
Another image transfer method consists in applying, by means of a support of special transfer paper having the same function of the above described printing fabric, a printed pattern by screen printing on a target surface. More specifically, the latter method provides that the image transfer is carried out at high temperature (i.e. at a temperature between 120.degree. C. and 180.degree. C.) and in a pressurized environment, for a period varying between 10 seconds and 15 seconds. This screen printing method is normally performed by means of a large size printing machine, with a treatment chamber, in which reproducing the pressure and temperature conditions required for the image thermal transfer is possible.
The combined action of pressure and temperature makes possible the drying of the inks used for printing and their fixing on the target surface.
To bring up the pattern on the target surface it is finally necessary removing the support of transfer paper from the chosen support.
The main types of heat transfer are known under the names of “SPLIT HOT” and “COLD PEEL” and differ from each other mainly by the application method.
The “HOT SPLIT” method provides that the transfer paper detaches immediately after the opening of the treatment chamber of the print machine. This involves the dissolution of the ink, still hot and relatively fluid, on the target surface, and, consequently, the formation of an image by not well defined contours. In this case, most of the ink remains attached to the target surface, while the remaining part remains adherent to the transfer paper.
A variant of the “HOT SPLIT” method briefly described above involves the use of a transfer paper, commonly known with the term “PUFF”. In this latter case, it is used an ink having the peculiar characteristic to expand under the effect of heat. The reasons, i.e. the resulting images, show reliefs, which makes this method particularly suitable for printing caps and T-shirts.
The “COLD PEEL” method provides, however, that both the application of the transfer paper on the target support, and the removal of the same from said support, are cold carried out. The ink transfer from the transfer paper to the substrate takes place, instead, hot.
In this case, unlike the “HOT SPLIT” method, the ink film is completely transferred from the transfer paper to the target support.
The papers used in the transfer “COLD PEEL” method are characterized by a plastic and bright appearance, and a marked opacity.
In general, it is possible to divide screen printing into four main categories (i.e. the textile screen printing, screen printing graphics, industrial screen printing and silk screen art), defined according to the types of product applications subjected to screen printing.
The textile screen printing comprises all the possible applications of the textile supports screen printing.
The graphic silk screen printing includes advertising, or illustrations, charts or drawings.
Industrial screen printing concerns, instead, the applications of functional decoration, and thus not only aesthetic.
Finally, the art screen printing regards the reproduction of works similar to the original.
The transfer technique, known from several years, provides that the images are printed with inks for the printing on plastic sheets.
The ink reproducing the image has the characteristic of a very low adhesion to the plastic sheet, because otherwise it could cause the transfer of the image from the plastic sheet to the target surface, by rubbing the sheet with pencil or rod.
Once the image is printed on said sheet of plastic, over the image it is applied, in succession, glue and then a silicone paper sheet with transparent protection function, to be removed at the time of the image transfer.
The above glue performs, instead, the function of allowing the adhesion of the image to the surface of the target support
Traditional screen printing techniques have, however, several limitations and drawbacks.
Known screen printing techniques do not allow, in fact, to decorate non-linear, or curved or variously shaped surfaces.
In addition to that, they often require the disassembly of complex products, which consist of several pieces, before subjecting them to the operations of screen printing.
Furthermore, for the decoration by screen printing of large products or supports, it becomes necessary the use of particularly bulky and difficult to install printing machines.
Japanese patent document no. JP-H056836A describes a multilayer capacitors manufacturing method, formed by the alternation of dielectric layers, made by a dielectric material paste, and electrode layers, made by conductive paste, in which these layers are overlapped to each other.
In particular, the method described in the aforementioned Japanese document has the primary purpose of obtaining very thin dielectric layers and electrodes from the uniformly flat surface, limiting the risk of short circuits of the electrode.
This method involves printing, by screen printing technique, a layer of paste of dielectric material on a support plane, from which this paste is then transferred on the side surface of a soft roll, formed for example by silicone rubber, by rolling the roller on the paste layer.
The dielectric material paste layer around the roller, is then imprinted on a flat surface, by rolling the roller itself on the latter.
At this point, always by means of screen printing technique, a layer of conductive paste (ink) on a support plane is printed, from which this paste is then transferred on the side surface of a roller as said above, by rolling it on the layer of conductive paste deposited on the plan support.
The layer of conductive paste around the roller is then embossed on the dielectric material paste layer previously deposited on the flat surface.
By repeating the operating steps described above, it is then obtained a compound formed by layers of dielectric material paste alternating with layers of conductive paste.
The composite thus obtained is cut so as to obtain individual multilayer capacitors, which are then dried and cooked.
Therefore, for realizing such multilayer capacitors, it is carried out the formation of layers, of different materials, according to the continuous operating procedure indicated above.
These layers have, in fact, a continuous pattern with no embedded design, image or particular representation.
From the above it appears evident the reason for which is not minimally addressed, in this Japanese patent document, the problem of transferring an ink layer representing an image or a drawing from a source support to a target support in a reliable way, i.e. without that deformations in the image or in the drawing transferred occur.